JP2815696B2 - Method of manufacturing hollow resin product having bent portion - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a hollow resin product having a bent portion.

[Prior Art] Conventionally, a method of manufacturing a hollow body product having a bent portion such as an intake manifold has been proposed. For example,
JP-A-63-92419 and JP-A-62-218115 disclose a method of manufacturing a bent tube using a vanishing core made of a low melting point alloy. However, this method consumes a large amount of mechanical energy required for casting a low-melting alloy core and heat energy required consistently in the process, and the core is heavy and difficult to handle. When an alloy, glass, or the like is used, there is a problem that the bent tube is easily broken, and particularly when the glass is crashed, the “bulk” increases sharply and the bent tube is deformed from the inside, and there is a risk that the bent tube is broken.

Japanese Patent Application Laid-Open No. 1-176529 discloses a hollow resin core in which resin parts preformed in a state of being divided into two parts are connected. However, this type of core has a problem with the joint. For example, in the case of welding adhesion, there is a possibility that a step is generated in a joint portion, burrs are generated, and thermal peeling is caused.

JP-A-61-202827 discloses a resin core in which inorganic fine particles such as sand are filled as a reinforcing material in a hollow portion of a hollow resin core obtained by blow molding. However, in blow molding, burrs must be cut off, and the wall thickness of the general part is limited to several millimeters, and it becomes even thinner at the bent part.Without internal reinforcement, it can withstand resin pressure and temperature when forming a bent tube Can not. When an internal reinforcing material such as sand is used, the core becomes dirty, and it is difficult to completely separate the core material and the internal reinforcing material. In this case, if a solid core is formed by injection molding, a reinforcing material is not required, but on the other hand, the discontinuity causes a dimple-like sink mark due to shrinkage of the resin. Also, if you try to remove the core after molding integrally with the bent tube, there are few exposed parts,
Core removal operations such as heating and solvent crash cannot be performed.

Japanese Patent Publication No. 54-15291 discloses a method for forming a thick article. If the core is manufactured by such a method, the core becomes hollow, and a heating solvent crash or the like is easy.On the other hand, the gas injection port has a thin core, and the flow terminal of the resin has a large thickness. Resin pressure and heat are applied to the bent portion when a bent tube is injection-molded, and the stress is maximized so that the core is easily deformed (see FIG. 6). To prevent this, it is necessary to reduce the hollowness of the core and increase the overall wall thickness, but this increases the amount of core material used, increases the core weight, This leads to inefficiency in the removal process.

[Problems to be Solved by the Invention] In view of such circumstances, the present invention uses a light-weight and easily-dissipating core that has a bent portion but does not deform under the molding conditions of a product, and has a high productivity. It is an object of the present invention to provide a method for producing a hollow product.

[Means for Solving the Problems] As a result of intensive studies, the present inventor has found that, after injecting a resin from at least two gates into the cavity in an amount equal to or less than its capacity, the incompatible fluid is immediately injected into the cavity to form a bent hollow. The present inventors have found that it is effective to form a partition wall as a reinforcing material in the portion, and have reached the present invention.

That is, the present invention relates to a method for producing a resin hollow product, which is a method for producing a resin hollow product having a bent portion comprising the following steps.

(1) A step of press-injecting a fluid that is incompatible with the resin into each molten resin in the injection molding step injected into the cavity from at least two gates.

(2) A step of pressing the inside of each resin to associate at the bent portion of the cavity, forming a partition wall at the associated portion, and molding a resin core.

(3) Insert this core into the resin shell mold,
A step of forming a resin outer shell portion on the outer peripheral portion while leaving the end portion of the core.

(4) A step of injecting a core material eroding fluid into the hollow interior from the end of the core to eliminate the core.

Examples of the core material used in the method of the present invention include polystyrene, high-impact polystyrene, polycarbonate, and a water-soluble resin.

In order to form a partition wall in the core of the present invention, the fluid to be injected during the injection molding may be any fluid that is incompatible with the core resin material, such as a gas such as nitrogen gas, carbon dioxide gas, or air. Alternatively, a liquid such as water can be used.

The present invention inserts a core having a partition wall at a bent portion inside the hollow into a mold to form a product by a conventionally known method, and the core can be removed by injection of a solvent after molding. . As this solvent, one that dissolves or penetrates the core material and causes cracks is used. For example, an organic solvent such as tetrachloroethane or isopropanol or water is removed when the core material is water-soluble, and the core is removed. Can be used as a solvent for The molding material for the bent tube produced by the method of the present invention includes, for example, an engineering plastic such as polyamide (nylon 6, 46, 66, etc.), polyphenylene sulfide, polysulfone, or a mineral reinforcing agent thereof, glass A reinforcing material such as a fiber reinforcing material or a composite material with another resin can be used. These have strong resistance to organic compounds such as gasoline and oil, and do not cause dissolution, cracks and the like.

FIG. 1 is a view showing the appearance of an intake manifold which is an example of a bent tube manufactured according to the present invention. Second
The figure shows the appearance of the core for that purpose.

Next, an outline of the manufacturing method of the present invention will be described with reference to the drawings.

FIG. 3 shows a core injection molding die used in the present invention. A gas injector is pushed into two locations, and a fluid that is incompatible with the core material such as the nitrogen gas is injected into the cavity from the gas injector.

First, a core forming resin is injected into the cavity from the nozzle with a resin amount of 40 to 80% of the cavity volume.

The resin enters the cavity from the two gates via the runner, but remains unfilled in the middle. Next, a fluid incompatible with the resin is immediately injected from the injector.
The state after the fluid injection is shown in the cavity of FIG. FIG. 4 is a detailed view thereof. As shown in FIGS. 3 and 4, the resin associates in the middle of the cavity and finally reaches a pressure equilibrium while pressing the weld. Then, the resin having no place to go forms a partition wall at the meeting portion. This partition wall can adjust the installation position by mutually adjusting the fluid injection pressure from each injector,
Further, the wall thickness can be changed by increasing or decreasing the amount of the injected resin.

Further, the above-mentioned partition wall has a rib-like wall even when the thin central portion is broken by fluid pressure, and this rib reinforces the bent portion, so that the partition wall may have such a rib shape. .

Using the core molded as described above, a process of manufacturing a hollow product having a bent portion by molding a resin is started. This molding process can be performed by a conventional molding method.

That is, the core is inserted into a resin shell molding die, and a resin shell is formed on the outer peripheral portion of the core by injection molding or the like except for the end portion.

The last step of the present invention is a step of removing the hollow core from the molded product.

First, a core exposed portion of a molded product having a bent portion is cut off with a cutter to open a hollow portion. The erosive fluid for core removal is injected from the opening toward the hollow interior (see FIG. 5).

When the fluid is injected, the core hollow inner wall and the partition wall have numerous cracks due to stress cracks, and the core can be crushed and removed from the product by applying vibration. At this time, when a steel ball is driven into the hollow portion, the partition wall can be broken first, so that the vibration crushing can be performed effectively. Also, if the upper and lower openings are closed and a steel ball is put inside and vibrated, the core can be more effectively crushed. After the core is crushed and removed from the product, the steel balls can be easily separated from the resin scrap with a magnet.

The core resin scrap removed from the product can be crushed to an appropriate size with a crusher, or repelletized and recycled for core molding. Also, when using a water-soluble resin for the core material and dissolving the core by dissolving it in water, the eluted resin is separated by adjusting the pH of the water in which it is dissolved, and recycled. Can be done.

[Operation] The bent portion of a hollow core used for molding a resin hollow product having a bent portion is easily deformed by resin pressure and heat load during injection molding (see FIG. 6). Since the strength of the core is improved by providing a partition wall, the core is not deformed by injection molding, and the hollow portion of the product is not distorted or narrowed.

[Example] Hereinafter, as an example of the present invention, a specific example in the case of manufacturing an intake manifold will be described.

Using the mold shown in FIG. 3, the polystyrene resin is applied from the two gates in an amount of about 50% volume of the mold cavity:
Immediately injected nitrogen gas at a pressure of 70 kg / cm ² and 6
Was injected at 0 kg / cm ^2, thickness 7mm having a bent portion inside the partition wall
Was formed.

Next, using this core, an intake manifold was formed by injection molding using nylon 66. After the molding, tetrachloroethane was injected into the core hollow and vibrated to remove the core material, thereby producing an intake manifold. In this intake manifold, no narrow portion was found even inside the bent portion.

[Effects of the Invention] As described above, according to the present invention, a partition wall is formed inside the bent portion of the core, and this acts as a reinforcing material for the bent portion that is easily deformed. To provide an inexpensive resin bent tube that can reduce the amount of core material used, facilitate the removal of the core, increase the productivity of the bent tube made of resin, promote energy saving, and reduce the cost. Can be.

[Brief description of the drawings]

FIG. 1 is a view showing an appearance of an intake manifold manufactured by the present invention, FIG. 2 is a view showing an appearance of a core for manufacturing an intake manifold, and FIG. 3 is an injection of a core used in the present invention. FIG. 4 is a view for explaining a molding die, and FIG.
FIG. 5 is an enlarged view of a part of FIG. A, FIG. 5 is a diagram illustrating a step of removing a core, and FIG. 6 is a diagram illustrating a case where a bent tube is formed by using a core having no partition wall in a hollow bent portion. FIG.

Claims (1)

(57) [Claims] 1. A method for producing a resin hollow product, comprising:
A method for producing a resin hollow product having a bent portion comprising the following steps. (1) A step of press-injecting a fluid that is incompatible with the resin into each molten resin in the injection molding step injected into the cavity from at least two gates. (2) A step of pressing the inside of each resin to associate at the bent portion of the cavity, forming a partition wall at the associated portion, and molding a resin core. (3) Insert this core into the resin shell mold,
A step of forming a resin outer shell portion on the outer peripheral portion while leaving the end portion of the core. (4) A step of injecting a core material eroding fluid into the hollow interior from the end of the core to eliminate the core.